Carbon solar abundance

We have selected several unblended CH lines located in the near-UV between 3145-3190 A modified their oscillator strengths (gf-values) by fitting the solar high-resolution spectrum and assuming solar abundance of carbon 8.56 from Anders and Grevesse (1989). These lines are measurable in dwarfs down to the metallicities —3. Our results are shown in the Fig. 1. We confirm the metallicity dependence of the C/O ratio (Tomkin et al. 1992, Akerman et al. 2004). On the other hand, our plot for C/O shows a steep rise at [0/H]< —1. It is not clear if this effect is real. The work is in progress to address this issue using other abundance indicators such as CH 4300 A and better quality spectra. 

SNII events alone explain the observed solar abundance distribution between oxygen and chromium. This can be taken as a major theoretical achievement. Complementary sources of hydrogen, helium, lithium, beryllium, boron, carbon and nitrogen are required, and these have been identified. They are the Big Bang, cosmic rays and intermediate-mass stars. Around iron and a little beyond, we must invoke a contribution from type la supernovas (Pig. 8.5). These must be included to reproduce the evolution of iron abundances, a fact which suggests... 

Finally, we mention the central star of NGC 246. This star is known to display CIV as the strongest absorptions in the blue spectrum and broad shallow lines of Hell hydrogen can not be detected (Heap, 1975 Husfeld, 1986). Analysis by Husfeld (1986) revealed that this CSPN is extremely hydrogen-deficient solar abundance of this element cannot be excluded. 

Natural isotopes of carbon and their solar abundances... 

The observational constraints on the solar isotopic abundances of oxygen are also poor. The only solar-wind measurement, by the Advanced Composition Explorer, yielded a ratio of consistent with the terrestrial value, with 20% uncertainty (Wimmer-Schweingruber et al., 2001). An earlier spectroscopic measurement of the solar photosphere gave a similar result (Harris et al., 1987). No information is available on the solar abundance. The very limited state of knowledge of the solar isotope abundances of carbon, nitrogen, and oxygen illustrates the importance of the NASA Genesis mission to collect a pure solar-wind sample and return it to Earth for laboratory measurement. 

The key processes for the formation of the simplest carbon-, oxygen- and nitrogenbearing molecules have been discussed extensively before (Dalg2imo iuid Bktck 1976 Watson 1978 Crutcher itnd Watson 1985 vein Dishoeck 1988), emd will be only briefly reiterated here. Since H and are so much more abundemt in interstellar clouds than any other species, the dominant reactions usually involve hydrogen, whenever possible. Table 2 lists the current best estimates of the solar abundances of the veirious elements relative to hydrogen. Some of the heavier elements are depleted from the gas phase in interstellar clouds. In diffuse clouds, this depletion is very mild and tends to exceed a feictor of four only for heavier metals like Ca, Ti, Mn, emd Fe. The freiction of the solar abundemce of element X in the gas phase is denoted by the depletion foctor Sx, with Sx < 1-... 

Water and carbon play critical roles in many of the Earth s chemical and physical cycles and yet their origin on the Earth is somewhat mysterious. Carbon and water could easily form solid compounds in the outer regions of the solar nebula, and accordingly the outer planets and many of their satellites contain abundant water and carbon. The type I carbonaceous chondrites, meteorites that presumably formed in the asteroid belt between the terrestrial and outer planets, contain up to 5% (m/m) carbon and up to 20% (m/m) water of hydration. Comets may contain up to 50% water ice and 25% carbon. The terrestrial planets are comparatively depleted in carbon and water by orders of magnitude. The concentration of water for the whole Earth is less that 0.1 wt% and carbon is less than 500 ppm. Actually, it is remarkable that the Earth contains any of these compounds at all. As an example of how depleted in carbon and water the Earth could have been, consider the moon, where indigenous carbon and water are undetectable. Looking at Fig. 2-4 it can be seen that no water- or carbon-bearing solids should have condensed by equilibrium processes at the temperatures and pressures that probably were typical in the zone of fhe solar... 

As evidenced by their low abundances, carbon compounds, water, and other volatiles such as nitrogen compounds were probably not significantly abundant constituents of the bulk of the solids that formed near the Earth. Many of the carriers of these volatiles condensed in cooler, more distant regions and were then scattered into the region where the Earth was forming. Eragments of comets and asteroids formed in the outer solar system still fall to Earth at a rate of 1 x 10 kg/yr and early in the... 

As can be seen in Fig. 2-1 (abundance of elements), hydrogen and oxygen (along with carbon, magnesium, silicon, sulfur, and iron) are particularly abundant in the solar system, probably because the common isotopic forms of the latter six elements have nuclear masses that are multiples of the helium (He) nucleus. Oxygen is present in the Earth s crust in an abundance that exceeds the amount required to form oxides of silicon, sulfur, and iron in the crust the excess oxygen occurs mostly as the volatiles CO2 and H2O. The CO2 now resides primarily in carbonate rocks whereas the H2O is almost all in the oceans. 

The volatile-trapping mechanism has a further problem associated with the temperature. Very volatile molecules such as N2, CO and CH4 are not easily trapped in laboratory ice simulation experiments unless the ice temperature is 75 K, which is somewhat lower than the estimated Saturnian subnebula temperature. This has led to the suggestion that the primary source of nitrogen within the Titan surface ices was NH3, which became rapidly photolysed to produce H2 and N2 upon release from the ice. The surface gravity is insufficient to trap the H2 formed and this would be lost to space. However, the origin of methane on Titan is an interesting question. Methane is a minor component of comets, with a CH4/CO ratio of clCT1 compared with the present atmospheric ratio of > 102. The D/H ratio is also intermediate between that of comets and the solar nebula, so there must be an alternative source of methane that maintains the carbon isotope ratio and the D/H isotope ratio and explains the abundance on Titan. 

The conclusions of Hurt s study of year-by-year oxygen isotope ratios in 72 years of S. gigantea are thus supportive of the conclusions of the CIAP study [49] that solar variations influence the abundances of many kinds of chemical species in the stratosphere, and therefore influence the.amount of solar energy they absorb and re-radiate to earth, and therefore influence the surface temperature of the earth and especially the surface temperatures of the oceans. It is the surface temperature of the oceans which produces the phenomena we have discussed the isotope ratio variations in rain and hence in tree rings, the isotope ratio variations in the Greenland ice cap, in the organic carbon and uranium concentrations in sea cores, and furthermore variations of the sea surface temperature produces variations in the carbon-14 to carbon-12 ratio fractionation at the sea air interface and hence in the carbon-14 content of atmospheric carbon dioxide and hence in the carbon-14 content of tree rings. 

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